There is a machining center forming a kind of column moving type machine tool as shown in FIG. 13.
In the figure, 1 is a bed, a top face 1a thereof is enlarged, and a column support face 1b is formed to a part of the top face 1a. Longitudinal guide rails 2, 2 are fixed on the column support face 1b. 
A slide 3 is slidably and displaceably engaged with the guide rails 2, 2 to move in a longitudinal direction f1 by a motor 4.
Lateral guide rails 5, 5 are fixed on the slide 3, and a column 6 is slidably and displaceably engaged with the lateral guide rails 5, 5 to move in a lateral direction f2 by a motor 7.
A spindle device 8 is longitudinally installed to the column 6 to vertically move on a fixed orbit through a motor 9.
In this case, the spindle device 8 comprises a longitudinal spindle 10 whose front end serves as an end for installing a cutting tool, a bearing cylinder 11 supporting the spindle 10, and a motor 12 for rotating the spindle 10.
A lateral standing cover wall 13 is provided close to the front face of the column 6 so as to prevent cutting chips and coolant from splashing. The cover wall 13 comprises lateral extensible cover walls 14, 14 fixed to right and left sides of the spindle 10, and a vertical extensible cover wall 15 provided on a vertical moving route for the spindle 10.
In this case, a lateral extensible cover wall 14 comprises a plurality of plates 14a superposed slidably and displaceably in a lateral direction, each plate 14a being formed by bending upper and lower ends of a metal plate in wedge shape. The cover wall 15 is formed by superposing a plurality of metal plates 15a slidably and displaceably in a vertical direction.
A box casing 16 is provided on the top face 1a of the bed 1 so as to cover the column 6. A space in front of the standing cover wall 13 inside the casing 16 forms a shielded machining space SK. A jig support table 17 for fixing jigs is installed in the anterior part of the shielded machining space SK.
A longitudinal extensible cover device 18 is installed at the front face of the slide 3 to cover the guide rail 2, comprising a plurality of angle metal plates 18a superposed slidably and displaceably in the longitudinal direction f1, keeping the guide rails 2, 2 covered regardless of longitudinal movement of the column 6.
Besides, an automatic tool changer (ATC) is provided at a suitable position, such as an upper portion of the box casing 16.
When machining a work with this machining center, for example, the work is fixed at a specific position on the jig support table 17, needed information is inputted to a not-illustrated control device, and thereafter, an operation is started. According to this, the required motors 4, 7, 9 operate to move the spindle 10 in the longitudinal direction and in the lateral direction or in a vertical direction. In this state, a tool installed at the tip of the spindle 10 rotates together with the spindle 10 by the motor 12 to automatically cut the work.
During this machining, cutting chips of the work are scattered to the circumference by rotations of the tool and the spindle. In case of coolant machining, in which coolant is fed during machining, the coolant is splashed, thereby scattering cutting chips.
Although the scattered cutting chips drop on the extensible cover 18 and the like, they never accumulate on the guide rails 2, 5 directly. In addition, the cutting chips going to the column 6 never go into from the front face of the column 6 to the rear side because they are intercepted by the lateral standing cover wall 13. Accordingly, the column 6 works smoothly in the longitudinal direction and in the lateral direction, and the spindle 10 works in the vertical direction without interruption.
In the above-mentioned conventional machining center, since the lateral extensible cover walls 14, 14 are respectively formed by a plurality of plates 14a superposed slidably and displaceably in the lateral direction, they need a comparatively large lateral space even if they are made, at the most, short. Therefore, the lateral length of the machine tool is comparatively longer than the lateral displacement of the column 6, which is contrary to the intent of a compact device. In connection with this, since the lateral width of the shielded machining space SK is enlarged, much time is required to remove the cutting chips. In addition, since the longitudinal extensible cover device 18 is formed by a plurality of angle metal plates 18a superposed slidably and displaceably in the longitudinal direction f1, the cutting chips enter a sliding portion of each angle metal plate 18a over time. Therefore, the sliding portion is prevented from moving smoothly and slidably.
The present invention aims to provide a column moving type machine tool with a shielded machining space for solving the above-mentioned problems.